Side moon

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A halo around the moon with two minor moons above the University of Alberta, Canada observatory on March 27, 2010. The moon was approximately 94% illuminated.

A side moon is a halo phenomenon that is caused by the refraction of moonlight on ice crystals in the troposphere .

Analogous to the sub-suns , the phenomenon occurs at a distance of around 22 ° on both sides of the moon, and usually only when covered with cirrus or cirrostratus clouds , but can in principle also be caused by ice crystals at a low altitude (e.g. polar snow ) become. Sub-moons are rarer than sub-suns, as the moon has a lower luminous intensity than the sun. They are therefore usually only visible when the moon is full.

See also: side sun